Apparatus for the fabrication of image display screens



March 1961 T. v. RYCHLEWSKI ETAL 2,976,838

APPARATUS FOR THE FABRICATION OF IMAGE DISPLAY SCREENS 2 Sheets-Sheet 1Filed July 29, 1957 ROBERT F. WILSON ATTORNEY March 1961 T. v.RYCHLEWSKI EI'AL 2,976,838

APPARATUS FOR THE FABRICATION OF IMAGE DISPLAY SCREENS 2 Sheets-Sheet 2Filed July 29, 1957 INVENTORS THAODEUS RYCHLEWSKi ROBERT F.W\LSON mimATTORNEY United States Patent APPARATUS FOR THE FABRICATION OF IMAGEDISPLAY SCREENS Thaddeus V. Rychlewski and Robert F. Wilson, SenecaFalls, N.Y., assignors, by mesne assignments, to Sylvania ElectricProducts line, Wilmington, Del., a corporation of Delaware Filed July29, 1957, Ser. No. 674,970

1 Claim. (Cl. 118-321) This invention relates to image display screensand more particularly to a method for forming such screens and to anapparatus adaptable for use in the screen fabricating process.

Image display screens of the type employed in color television apparatusgenerally comprise a transparent viewing panel having a large number ofdiscrete triad patterns formed thereon. Each pattern usually consists ofbars, dots or stripes of red, green and blue color fluorescingmaterials. A screen of this type may be fabricated by a photographicprinting technique wherein a photosensitive material is used to bind thefluorescent material to the panel. In such a process, the transparentviewing panel is first coated with a thin film of a photosensitivesubstance, and a dry powdered fluorescent material is subsequentlydeposited thereon. The panel is then exposed to light through anappropriate negative to cause the photosensitive material to harden andadhere to the panel. Those portions of the screen which were not exposedto light are subsequently removed by dissolving the material with asuitable solvent. This procedure is repeated for each fluorescentmaterial pattern used in the display device.

In a screen forming process of the type described above, thephotosensitive material has heretofore been applied by a manual sprayingoperation wherein the operator endeavors, through a series of movements,to achieve a uniform photosensitive material coating. However, due tothe inherent inaccuracies involved in such a procedure, thephotosensitive film has been found to be nonuniform in thickness and inwetness over the panel. When the photosensitive film is too wet or toodry in given areas, the powdered fluorescent material will not adhereuniformly over the panel, and a fluorescent material pattern will beformed which is more thick or better adhering in some areas than inothers. In addition, if the photosensitive material coating thickness isnot uniform, the amount of light needed to harden or make insoluble oneportion of this material will not be sufficient to harden otherportions. Screens which are fabricated on a panel which has anon-uniformly thick photosensitive material coating produces patternswhich are unacceptable since the thick portions of the coating may notcompletely harden and may therefore be dissolved by the solvent.

Accordingly an object of the invention is to reduce the aforementionedditficulties and to provide improved fabrication procedures for imagedisplay screens.

A further object is the production of a high quality image displayscreen having good fluorescent material pattern uniformity.

Another object is the provision of improved means for fabricating animage display screen.

A'still further object is the provision of improved means adapted to beemployed in the process of fabricating image display screens.

The foregoing objects, as well as other objects which will be apparentafter reading the following description,

F ice taken in conjunction with the accompanying claim, are achieved inone aspect of the invention by the provision of a process forfabricating screens wherein the photosensitive material is sprayed uponthe panel in a series of spray passes which move back and forth acrossthe panel, the spray device and panel being oriented in a differentposition relative to one another for each spray pass. An apparatusformed to provide oscillatory movement for the spray device in additionto means for rotating the panel relative to the spray device is providedto facilitate the application of a uniform photosensitive materialcoating to the panel. After the spraying operation has been completed,the fluorescent material is deposited upon the photosensitive coatingand the panel is exposed to light through anegative to form the pattern.A developing fluid is subsequently applied to the panel to achieveremoval of the unexposed portions of the photosensitive material. Thisoperation is repeated for each of the color fluorescing materials, withproper off-setting of the light source from the axis of the panel foreach exposure operation. to produce the complete pattern.

The fluorescent materials employed in the screen may be any conventionaltype of electric field and/or electronresponsive inorganic material suchas those formed from sulfides, oxides, tungstates, aluminates,phosphates s'ilicates or selenides of one or more metals consisting ofzinc, cadmium, berryllium, magnesium, manganese, calcium, strontium andothers well known in the art.

The photosensitive or light hardenable substance may comprise any wellknown formulation which is rendered non-dispersible or substantiallyinsoluble in a suitable developing fluid. Among the materials adaptedfor use in the production of image display screens are photographicgelatins, polyvinyl alcohol, polyvinyl acetate and polyvinyl pyrolidonesensitized with such substances as ammonium, potassium or sodiumdichromates, monomeric type dye-sensitized polymers, and a variety ofcommercial lacquers. such as Kodak Photosensitive Lacquer (KPL) andKodak Photoresist (KPR) which has incor porated therein a volatilesensitizer.

The solvent or developing fluid used in the process is dependent uponthe choice of photosensitive material which is employed. For instance,an organic solvent such as trichloroethylene or a ketonemay be used withcommercial photosensitive lacquers and with polyvinyl acetate whereasother substances such as polyvinyl alcohol are water soluble.

For a better understanding of the invention, reference is made to thefollowing description taken in conjunction with the accompanyingdrawings in which:

Fig. 1 is a partially cut-away perspective view of a spray apparatus;

Fig. 2 is a plan view of a spray head adapted to be employed with theapparatus shown in Fig. 1; I

Fig. 3 is a flow diagram of the spray technique'used in one aspect ofthe invention; and a Figs. 4 and 5 illustrate two positions of the sprayhead during movement thereof in the screen forming process.

Referring to the drawings, the screen is formed upon the internalsurface of a curvilinear glass face plate 11 of a conventional viewingpanel 13 which may be employed in a cathode ray tube. The face plate maybe initially flow, spin or spray coated with a bonding substance such asdilute solution of polyvinyl alcohol, which is capable of being renderedlight hardenable or photosensitive. This preliminary coating serves toprovide good adherence between face plate 11 and the screen material tobe later applied. The light hardenable material may be sensitized, ifdesired, and it may be removed after a prescribed time by a developingfluid such as deionized water. It has been found that even in thoseinstances where the preliminary coating has been rinsed with a aeraaasdeveloping" fluid or solvent," averythin' remains on the face plate toprovide aisurface which is capable of bonding the screen pattern totheface plate.

'After applicationbf'the initial. coating, the panel is sprayed with asolvent dispersible light hardenable substance such-as polyvinyl alcoholsensitized with ammodichromateto form a coating which is uniformly thickand uniformly wet over the entire face plate area. The spray device 15is formed to provide a substantially spheroidal diploid pattern 17, Fig.3D, which has a length larger than the lateral dimension of the viewingpanel. The center of spray pattern 17 is offset from the center of thepanel to prevent an accumulation of light hardenable material at itsmid-portions, and a plurality of spray passes are utilized in a backwardand forward motion while providing relative movement between face plate11 and spray pattern 17 intermediate each reciprocating spray patternmovement. Referring particularly to Fig. 3, it can be seenthat the spraypattern travels along its first course, which is offset from the centerof face plate 11, to cross the panel from right to left. After thisinitial pass, panel 13 is rotated approximately 60 counterclockwise andspray device 15 reverses its direction so that spray pattern '17 moves"from left to right along a path which is again offset from the center offace plate 11. This procedure may be repeated for a total of six passes,each one being in a direction opposite to the previous pass, and withface plate 11 being rotated approximately 60 intermediate the subsequentspray device movements. The cross-sectional shape of pattern 17 is suchthat on oppositely disposed passes, e.g., passes l and 4, the broaderportions of the spheroid on pass Number 4 covers the panel area whichwas coated by the more narrow portions of the diploid on pass Number 1.Such a pro cedure provides an even distribution of the coating material. "Fig; 30) illustrates a. summation of' the spray pass locationsused to complete the sensitized polyvinyl alcohol coating. However, itis to be understood that more or less than six spray passesmay beemployed, if desired. 'For' instance, it has been found that. fourpasses 90 apart will also provide a uniform coating. However, as thenumber of passes. increase, the thickness of the coating increasesand'the light sensitive material is more diflicult to be made'insoluble.upon exposure to light. Conversely, as the number of passes decreases,the ability to acquire a uniform coating decreases. T In any event, ithas been found to be preferable to arrange the direction of spraymovements. symmetrically about panel 13. The utilization of such amethod provides a more uniformly thick and more uniformly wet coatingthan has heretofore been achieved. Since the spray pattern 17 is largerthan panel 13, there is complete coverage on each pass even though thecenter of'the pattern is offset from the center of the faceplate. Inpractice, this method may be efficiently employed by mounting spraydevice 15 for oscillatory movement about a point which is located at aposition approximately the distance of the face plate radius from theface plate and offset a me scribed distance from the longitudinal axisof panel 13. To provide the relative movement between the panel andspray device 15, the panel may be mounted for rotation about its ownlongitudinal axis.

After application of the light hardenable sensitized polyvinyl alcoholcoating, a fluorescent material such as the electron excitable greenphosphor, zinc ortho-silicate, isiapplied to the coating. This phosphormay be deposited by a dusting technique wherein the phosphor, in drypowdered form, is introduced into the atmosphere above the panel andallowed to settle in a uniform manner upon the. tacky surface of. thesensitized polyvinyl alcohol. Subsequently, an appropriate negativehaving aform-which will produce the desired bar, dot or stripe patternconfiguration, is spacedfrom the coated panel surface-and thephotosensitive material and adhering phosphor are exposed'throughthenegative, to

light radiating from a point source. 'the screen which have been exposedto light become Those portions of hardened and adhere to the glass faceplate 11. After exposure, the screen is washed with a developing fluidor solvent such as deionized water to remove the unexposed portions of.the photosensitive. substance and fluorescent material coating.

The above described process may then be repeated with the successiveapplication of red and blue color fluorescing materials, with properofi-setting of the light source relative to the panel axis for eachexposure operation. Zinc phosphate is a commonly used red phosphormaterial while a zinc sulphide has been found to be an acceptable bluephosphor material.

The preliminary coating of polyvinyl alcohol described above isgenerally only used prior to the application of the first phosphorpattern. That is, a dilute solution of this material is usually notapplied intermediate the successive screen pattern forming processes.However, the spray application of sensitized polyvinyl alcohol whichserves to form the tacky surface upon which the phosphor materials aredeposited, is used to form the surface or adhering medium for eachphosphor material employed in the tube.

Referring to Figs. 1, 2 and 3, an apparatus for applying the sensitizedlight hardenable material is shown comprising a table 19 upon which thepanel 13 is positioned, and a hood 2]. providing an enclosure whereinthe spray coating process is preformed. An exhaust port 23 is formed inone wall of hood 21 to provide an escapcment for the fumes generatedduring processing. Panel 13 is positioned upon a holder or rotatableplate 25 and is held thereto by means of friction devices 27. This plateis mounted upon the upper surface of sleeve 29, which is telescoped overshaft 31. A nut 33 is threaded upon the lower portion of shaft 31 toposition plate 25 upon table 19. This thread able engagement allowspanel 13 to be raised or lowered relative to device 15. A plurality ofpositioning pins 35 are mounted upon the shaft to extend radiallyoutward therefrom in a symmetrical orientation about the peripheralsurface thereof in accordance with the symmetrically disposed spray passdirections illustrated in Fig. 3. A

spring loaded locking device 37, which is biased down- 0 wardly, isslidably mounted upon sleeve 29 so that the lower curvilinear surface 39cooperates with pin 35 to hold panel 13 at each prescribed position. Inoperation, the panel is rotated from one pin position to the next aftereach reciprocating movement of the spray device 15. During thismovement, the edge of locking device 37 rides over the pin and surface39 slides into engagement with the pin. Therefore, after the panel hasbeen positioned upon rotatable plate 25, and after one spray pass hasbeen made, the panel is rotated approximately 60 to the following pinlocation in readiness for the reciprocating spray pass.

Spray device 15 is mounted above panel 13 by means of cylinder 41,bracket 42, and shaft 43. The spray device is afiixed to the shaft sothat it may be moved through as oscillating motion back and forth acrossthe panel. The cylinder may be made adjustable upon shaft 43 to providelongitudinal or rotational positioning of the spray device relative toshaft 43. In addition, bracket 42 is provided with a slot 44 to allowmovement of the spray device to- Ward or away from panel 13.

Referring to Fig. 2, spray device 15 is shown, by way of example, as anexternally mixed pressure type feed gun having a nozzle 45, fluid intakeport 4'7, process air intake port 49 and an air control port 51. Thespray gun employs a needle valve which is controlled by the air pressureconnected through port 51 to regulate the operation of the device. Thiscontrol air pressure is intermittently applied to the needle valve whilethe process air and fluid are continuously applied to the gun. Duringthe photosensitive material coating operation illustrated in Fig. 3, theneedle valve allows the spray fluid to issue from nozzle 45 only duringthe oscillatory movement of device 15. However, it is to be understoodthat a continuously operating spray device may be employed, if desired.Also, spray guns which operate upon principles other than air pressuremay be utilized in the apparatus.

A brace 53, which is mounted upon a movable support frame 55, serves toposition shaft 43 and its attached cam wheel 57. The cam wheel isconnected through belt 59 to a driving wheel 61, which has a drive shaft63 connected to a gear reduction coupling 65 and a reversible electricmotor 67. When in operation, the motor will cause rotation of shaft 63to impart movement to cam wheel 57 and thereby cause spray device tomake a spray pass in one direction. After the spray device has reachedthe limit of its travel in one direction, the motor will be stopped in amanner to be hereafter described. Subsequently, the motor will bereversed in direction to cause spray device 15 to reciprocate.

The limit of movement of spray device 15 in either direction iscontrolled by the rotatably mounted cam wheel 57, which is provided withraised cam surfaces 69 formed to operate upon and press inwardly theplungers 71 of micro-switches 73. A series electrical connection may beprovided between the motor 67, each switch 73 and each positon of anappropriately connected double pole, double throw switch 75 so that themotor circuit will be opened when the appropriate plunger 71 rides uponcam surface 69 to thereby stop movement of spray device 15. Throwing theposition of switch 75 in the opposite direction to connect the oppositeswitch pole will energize the motor windings to cause rotation in theopposite direction so that spray device 15 will reciprocate to the pointwhere the other cam surface 69 moves beneath the other plunger 71 toagain open the motor circuit. Figs. 4 and 5 illustrate the relativepositions of the spray device and cam surfaces 69, and the manner inwhich cam wheel 57 rotates to bring the cam surfaces under plungers 71to limit the travel of the spray device during its oscillatory motion.

The air pressure utilized in the apparatus has an inlet 77 which leadsthrough line 78 to a fluid tank 79, to an electrically operated solenoidvalve 81 through line 82, and to the process air intake port 49 throughline 50. Air pressure is continuously maintained at tank 79 and at port47 whereas the air supplied to control port 51 is intermittently appliedby the valve 81 through line 84. When switch 75 energizes motor 67 ineither direction, it also energizes valve 81 through electrical lead 83to provide spray operation of device 15. When the appropriate switch 73is opened by cam surface 69, the electrical solenoid valve is alsodeactuated to stop the spray flow of polyvinyl alcohol. The fluid iscontinuously supplied to intake port 47 of spray device 15 through line85. Electrical connections are made to motor 67, valve 81 and switchfrom a junction box 87.

The apparatus shown in Fig. 1 serves to coat panel 13 with a uniformlayer of the photosensitive material. With the panel in the positionshown, switch 75 is moved to the right to complete the series circuitthrough motor 67, and valve 81 to thereby start the motion of the spraydevice and initiate the flow of spray fluid from nozzle 45. When thespray device reaches the end of its travel, the cam surface 69 has movedbeneath plunger 71 to open the series circuit and thereby stop theoperation of the motor and the spray device. Panel 13 is then rotated tothe next position where locking device 37 moves into cooperation withthe next positioning pin 35. The switch 75 is then thrown in theopposite direction to again energize motor 67 and device 15 to repeatthe spray application in a reverse motion. This procedure may berepeated six times in accordance with the process illustrated in Fig. 3.

It is to be understood that the pressure and fluid systems mayincorporate filters, valves, regulators, meters, etc., which willfacilitate accurate control of the pressures involved and a high degreeof p1u-ity for the photosensitive material used in the process.

Although several embodiments of the invention have been shown anddescribed, it will be apparent to those skilled in the art that variouschanges and modifications may be made therein without departing from thescope of the invention as defined by the appended claim.

What is claimed is:

An apparatus for spray coating an article having a com cave surface witha given average radius of curvature comprising a fixed vertical support,a horizontal holder rotatably mounted on the support, a spray devicemounted on a horizontal shafit above the support for oscillatory movement about the shaft, the spacing between the spray device and theholder approximately the radius of curvature of said concave surface andthe position of the spray device on the horizontal shaft being eccentricto the vertical axis of the support, reversible means for driving saidspray device through the oscillatory movement, and means for limitingthe travel of said reversible driving means in each direction.

References Cited in the file of this patent UNITED STATES PATENTS

